Since 1987 average temperatures in the West have been nearly 2F (1C) warmer than they were from 1970 to 1986, he and his colleagues found.

During that same 1987-2003 period, "we had more large fires," said climate scientist and study leader Anthony Westerling.

The later period had four times as many major fires as the slightly cooler 1970-to-1986 period. In addition, the average amount of land burned annually during the 1987-to-2003 period was 6.5 times greater than during the earlier period.

The years with the hottest temperatures also saw the most major forest fires and the largest tracts of burned land.

The findings fit with other recent studies.

"In Canada our area burned has almost tripled in the past 30 years," said Mike Flannigan of the Canadian Forest Service in Sault Ste. Marie, Ontario.